This invention relates to fire resistant glazings and to methods for the production of fire resistant glazings.
Fire resistant glazings generally comprise laminated structures having at least two transparent panes and at least one fire resistant interlayer. The transparent panes are normally glass panes although other transparent materials such as polycarbonates may be used. The interlayer must be optically clear and must remain clear without discolouration throughout the lifetime of the glazing. It must also function so as to improve the fire resistance of the glazing.
In many countries regulations exist specifying the fire resistance to be exhibited by a glazing intended for use in a particular location. Generally these regulations specify either a minimum time for which the glazing must form a barrier to the propagation of a flame when one side of the glazing is exposed to a fire and/or a minimum time for which the temperature and/or the intensity of radiated heat on the side of the glazing which is not exposed to the fire must remain below a specified figure. Glass panes will not meet any or all of these requirements and the fire resistant glazings which have been developed are laminated glazings having at least one interlayer between at least two opposed glass panes.
One type of interlayer which has been developed is based upon an alkali metal silicate waterglass. These silicate interlayers intumesce upon exposure to heat to form an opaque foam. The foam serves to assist the retention of the glass panes and acts as a barrier to radiant heat.
One method for forming a silicate based interlayer is to pour a waterglass solution on to the surface of a glass pane and dry the solution under controlled conditions to form a thin layer on the glass. A second pane may be placed on top of the dried interlayer to form a fire resistant glazing. Such processes are in use in the production of fire resistant glazings such as those sold by the Pilkington Group of companies under its trade marks PYROSTOP and PYRODUR.
A second method of forming a fire resistant glazing comprising a silicate based interlayer is the so called cast in place method in which a silicate solution is introduced into the space between two opposed panes and cured to form an interlayer. In a cast in place process the water content of the solution is retained in the cured interlayer. This high water content can absorb significant quantities of heat during a fire but can lead to failure caused by the generation of steam. A difficulty inherent in cast in place processes is the balance between the need for the solution to have a low enough viscosity to be poured into the space between two opposed glass panes and the need to cure that solution to form an interlayer which is sufficiently rigid to be retained in position through the lifetime of the glazing.
EP 590978 describes a cast in place process for the production of a fire resistant glass wherein the interlayer comprises an aqueous gel comprising an acrylamide polymer and a particulate metal oxide is produced by introducing a dispersion comprising an acrylamide monomer, the particulate metal oxide and a photopolymerisation initiator between the glass panes and irradiating the dispersion thereby polymerising the monomers. The fire resistance of the glazings produced is insufficient to meet the requirements of many of the regulations governing the use of fire resistant glazings.
EP 620781 discloses a method for producing a fire resistant glazing comprising a silicate based interlayer using a cast in place process and glazings produced by that process. The interlayer is produced by pouring a solution which comprises an alkali metal silicate wherein the molar ratio of silicon dioxide to alkali metal oxide is greater than 4:1 and from at least about 44% to 60% by weight of water between two glass panes. The solution comprises silica acid as curing agent. After pouring the composition is allowed to stand until it self cures to form a polysilicate. It is suggested that a wide variety of organic and inorganic compounds could be used as curing agents or as supplementary curing agents in small quantities provided that they do not form an insoluble precipitate when mixed with the silicate. There is no specific disclosure of any curing agent other than silicic acid.
EP 981580 discloses a method for producing a fire resistant glazing comprising a silica based interlayer using a cast in place process and glazings produced by that process in which the interlayer is obtained by pouring a solution which comprises at least 35% by weight of nanoparticulate silica, from 10 to 60% by weight of a polyfunctional compound such as a polyol and from 1 to 40% by weight of a solvent which is preferably water between two glass panes. The polyfunctional compound is said to give rise to a degree of cross linking of the silica particles. The preferred polyfunctional compounds are polyols.